1. Field of the Invention
The invention relates to an access box for one or more optic fibers in a tensioned cable.
This type of box can be used firstly to carry out a branch connection of optic fibers along their passage and, secondly, to modify the configuration of an optic fiber distribution network in an infrastructure of buildings.
The present invention can be applied especially to the setting up of optic fiber telecommunications networks in layouts for buildings, groups of buildings, and other business customer sites.
2. Description of the Prior Art
Cable configurations in buildings are generally of the tree-and-branch type and are not protected.
Indeed, a tree-and-branch type configuration of this kind generally uses copper or optic cables for the passage of fibers on paths going from point to point. All these cables leave from a given starting point and get distributed towards a plurality of arrival points. It is clear that this type of infrastructure is extremely vulnerable to accidental breaks in a cable.
However, another configuration can be made to secure the network through the technique of branch connection on a looped cable route.
In general, making a branch connection is an operation in which one or more wires or fibers of a passing cable are branched in order to be connected to another cable.
The branch connection technique is a relatively recent technique for optic fibers in which the optic fiber or fibers to be branched are cut in order to be connected to other fibers in another cable, known as a stub cable.
This technique has been developed by the present Applicant with the Flexible Optical Networks (ROF or Reseaux Optiques Flexibles). Reference may be made to the diagram of FIG. 1 which illustrates the principle of making branch connections on this type of network.
For a clearer understanding of the invention, we shall first of all recall the development of the structure of currently available optic fibers.
The first cables specially designed for making inter-city networks were cables with grooved rods.
Later, the technique of tubed cables was developed in order to better protect the fiber and to encase it. These tubes replace the grooves and protect the fibers more efficiently.
The method of manufacturing tubed cables is more advantageous and costs less than the method of manufacturing grooved cables. These cables are illustrated in FIGS. 2A and 2B which respectively show a view in perspective and a sectional view.
These cables were used to set up inter-exchange links. They were connected by both ends and were very often used over great distances (for inter-city connections, to set up what are known as national networks).
Thereafter, a new approach to distribution was envisaged for setting up networks in urban areas. This led to Flexible Optical Networks (ROF).
These networks which are looped, and therefore secured by a return along a different route, give improved reliability. They are used for providing connections to large corporate entities such as banks.
Connections for business customers have been developed very recently, most usually in urban areas, with the use of the branch connection technique.
One development, related to increasing expertise in manufacturing techniques and falling costs, has given rise to two designs of cables known as single-tube cables or distribution cables. These cables have optical characteristics substantially equal to those of inter-city network cables but have reduced weight (the weight is halved for the same diameter) and a greater number of fibers (four to five times more fibers).
Cables of this kind are illustrated in cross-section views in FIGS. 2C and 2D.
Unlike inter-city transport cables, the structure of the single-tube cables is characterized, for cables that may contain up to 288 fibers, by a thick high-density polyethylene tube in which two or four carriers or xe2x80x9cstrength membersxe2x80x9d are placed cross-wise. These strength members are made of fiberglass composite or aramid yarn and have a role of stabilizing the material. Both their tensile strength and their compressive strength facilitate laying.
The optic fibers are sheathed in groups in flexible modules.
The encasing of the fibers forming the single-tube cables results in two types of optical modules, namely: flat-cable fibers and flexibly encased fibers.
ribbon fibers or flat-cable fibers which are illustrated in FIG. 2C are encased side by side in a polymerized sheathing. This encasing, done during manufacture, facilitates the ground connection.
Flexibly sheathed fibers are encased in bulk, and are commonly called micro-ducts. They are illustrated in the drawing of FIG. 2D. These fibers are loose in this sheathing which is colored. The association of several sheathings is close to the prior art used for a copper cable. The color-coding makes it possible to identify a module at the end, and also within a cable section.
Conventionally there are two types of optic fiber connections.
A first type of connection consists of fusion splicing, solder splicing or splicing by mechanical means. The optical cores are aligned and the optic fibers can be placed in V-grooved supports or in ferrules. This type of connection is characterized by the fact that it cannot be dismantled.
The second type of connection consists of the use of connection elements. Optic fibers are held in dismountable devices that are aligned so as to align the cores of the fibers.
A connection by splicing makes it necessary to plan for excess cable length so that the splice can be cut and the connection modified.
A branch connection is added to the network by means of boxes designed for national networks. The role of these boxes is to provide for the mechanical and optical continuity of the cable in the connection areas. There are different kinds of boxes.
Base connector boxes enable the insertion of the cables into tubings. The optic fibers are organized inside the box and a dome or a cover protects the unit. These boxes are used in most of the English-speaking countries.
Bucket (or tray) type boxes are often prism-shaped. Cable passages are positioned so as to be opposite each other. In the continuity of the cable passage, an anchoring system is used to make all the cable strength members continuous. There are therefore as many anchorings as there are cables.
These cables can enter by either side of the box through various sealed tubings or passages. The cable crossing is located in the same plane as the joint plane of the box. The entire box therefore has to be enclosed, usually by means of resins for tight sealing. The fibers can be accessed only by completely disassembling the box and opening the joint plane.
The two cable ends enter the box in a widely sized space, and the bundle of fibers is coiled in cartridges or trays positioned in the box.
A box of this kind, designed for use in line with an over-length of cable on each side is increasingly being used in a herringbone pattern, i.e. with the cables entering by only one side.
Two other boxes have been described in order to adapt the branch connection to the most recent cable structures:
One box which has been the object of the patent application No. FR 96 07887 is characterized by its round shape. The over-length of cable is wound on the perimeter, so that the connection can be made outside the pulling chamber. This box can be upgraded by the assembling of one or more base connectors.
The primary drawback of a box of this kind is that it cannot be made on an industrial scale. It is designed for making branch connections on cables that are flexible so that they can be wound. The reduction in of the volume of the anchoring and the integration with tight sealing is valuable but costly. Furthermore, it is necessary to have cavities to accommodate the anchorings.
Another branch connection box, in the form of a tray as in the above description, consists of two symmetrical elements. This box is valuable because it is more compact and also because it uses mechanical tight sealing. In practice, this box is a developed version of the tray-type boxes described here above and has the same drawbacks.
Indeed, it has cumbersome anchorings and coiling structures that are not justified since only a few fibers need to be organized in the case of a branch connection. The strength member of the cable is cut up and reconstituted by the anchoring in the box. This gives rise to lengthy operations.
The coiling area or fiber access area does not facilitate the ergonomy of the connection. Indeed, in the case of a branch connection, it is desirable to have a length of at least 80 cm (40 cm on each side).
In short, with the existing boxes, the mechanical elements of the cable have to be reconstituted after having been cut. The anchoring operation gives rise to bulky and costly devices and introduces complexity into the designing of the boxes.
Most of the boxes presently available in the market do not provide for the possibility of making a branch connection from a passing optic fiber in a tensioned cable.
Furthermore, the existing branch connection boxes use connections made by the splicing of branched fibers. As a result, unnecessary fibers are left in the network. In addition, it is impossible to modify these connections.
Furthermore, there is no access box that can be used to modify the configuration of the fiber network after the infrastructure of the network has been installed, since all the connections are made by soldering and since the ergonomy of the box does not allow it.
An aim of the present invention is to overcome the drawbacks of the prior art.
To this end, the present invention proposes an access box comprising a connection system area for the shuffling and/or branch connection of a plurality of optic fibers.
The connection system area can furthermore be accessed at any time during and after the laying of the cable.
A more particular object of the invention is an access box for one or more optic fibers in a tensioned cable, the box comprising a structural section that integrates the passing cable and having a central connection system area demarcated by two connection bases to which there are connected a plurality of cleaved optic fibers, said connection system area having a plurality of mini-cables providing for the shuffling of the cleaved optic fibers and/or a plurality of branching cables providing for the branch connection of the cleaved optic fibers.
According to one characteristic, the box furthermore comprises anchoring areas located at each end of the structural section, each anchoring area comprising a spacer enabling access to the optic fibers of the cable.
According to one particular feature of the invention, the sheath of the cable is axially cut into two half-sheaths so as to release the optic fibers, each spacer device having two side cavities for the passage of the half-sheaths and a central cavity for the passage of the released optic fibers.
Each anchoring area has an anchoring cap.
According to another characteristic, the box furthermore comprises an area for the passage of the non-cleaved optic fibers located beneath the connection system area.
The passage area comprises an optic module cap.
The connection system area has a connection system cap, said cap being removable.
According to another characteristic, the box furthermore comprises two coiling areas that bracket the connection system area and are capable of receiving the cleaved optic fibers.
Each coiling area defines a volume demarcated by each connection base and by flanges attached to each side of the structural section.
Each coiling area has a safety cap.
According to one particular feature, each flange has a first groove in its upper part capable of working together with the safety cap.
According to another particular feature, the spacing between the flanges is maintained by one or more distance sleeves.
According to another characteristic, the box furthermore comprises a branch connection cap covering the cables branched between the connection system area and the end of the structural section.
According to one particular feature, each flange has a second groove above the first groove capable of working with the branch connection cap.
According to another characteristic, the structural section, when seen in a sectional view, has a U shape partially closed to form a slideway.
The box according to the invention has the advantage of reconstituting the protection of the cable in the work area and eliminates the drawbacks of the prior art, especially by preserving the integrity of the cable sheathing.
Indeed, the anchoring areas preserve the cable sheathing after it has been cut into two half-sheathings that cross the access box of the invention without a break and without hampering access to the fibers.
The invention furthermore retains the continuity of the optic fibers and provides for a limited hierarchy of the branch-connected fibers without any management and organization device.
No optic fiber section is left in the network after the branching of an optic fiber.
The invention can be used in service ducts (vertical or horizontal cableways) given the small cross-section of this box whose axis is coincident with that of the cable.
Furthermore, these access boxes do not require costly over-lengths which are difficult to manage and exploit.